1. Technical Field
The present invention relates to a wavelength variable interference filter which selects light having a desired target wavelength from incident light and releases the selected light, an optical module which includes this wavelength variable interference filter, and a light analyzer which includes this optical module.
2. Related Art
An optical filter (wavelength variable interference filter) which includes a pair of substrates each of which has a mirror disposed on a surface of the substrate on the side facing to the mirror of the other substrate is known (for example, see JP-A-2010-204457). This type of wavelength variable interference filter causes multiple interference of incident light between the pair of the mirrors, and allows only transmission of light having a particular wavelength and intensified by multiple interference.
A wavelength variable interference filter disclosed in JP-A-2010-204457 is provided with a first substrate and a second substrate disposed so as to be opposed to each other. An annular groove is formed on the surface of the first substrate on the side not facing to the second substrate so that a cylindrical movable portion positioned at the center of the first substrate and an annular diaphragm coaxial with the movable portion can be defined by the groove. A pair of electrodes are disposed so as to be opposed to each other between the pair of the substrates. Mirrors are provided both on the surface of the movable portion on the side facing to the second substrate and on the second substrate in such positions as to be opposed to each other. According to this structure, the diaphragm bends by the force of electrostatic attraction generated in response to voltage applied to the pair of the electrodes, and shifts the movable portion to which the mirror is attached in the thickness direction of the substrate for control of the gap between the pair of the mirrors. By this mechanism, the wavelength variable interference filter can select and transmit only light having the particular wavelength corresponding to the gap.
According to the wavelength variable interference filter disclosed in JP-A-2010-204457, the diaphragm is only provided on the first substrate. In this structure, reduction of the thickness of the diaphragm or enlargement of the area of the diaphragm in the plan view as viewed in the thickness direction of the substrates is required when the gap is desired to be narrowed by a large displacement amount of the movable portion. However, the diaphragm whose thickness is decreased or whose area is increased easily moves, and therefore the mirror provided on the movable portion easily shifts as well. In this case, the gap between the mirrors varies by external factors such as vibrations received from the outside, which possibly makes it difficult to provide the desired gap between the mirrors in correspondence with the applied voltage.